| Summary: | In plants, prolonged exposure to ultraviolet (UV) radiation causes harmful DNA lesions. Nucleotide excision repair (NER) is an important DNA repair mechanism that operates via two pathways: transcription coupled repair (TC-NER) and global genomic repair (GG-NER). In plants and mammals, TC-NER is initiated by the Cockayne Syndrome A and B (CSA/CSB) complex, whereas GG-NER is initiated by the Damaged DNA Binding protein 1/2 (DDB1/2) complex. In the yeast <i>Saccharomyces cerevisiae</i> (<i>S. cerevisiae</i>), GG-NER is initiated by the Radiation Sensitive 7 and 16, (RAD7/16) complex. <i>Arabidopsis thaliana</i> has two homologues of yeast RAD16, At1g05120 and At1g02670, which we named AtRAD16 and AtRAD16b, respectively. In this study, we characterized the roles of AtRAD16 and AtRAD16b. <i>Arabidopsis rad16</i> and <i>rad16b</i> null mutants exhibited increased UV sensitivity. Moreover, AtRAD16 overexpression increased plant UV tolerance. Thus, AtRAD16 and AtRAD16b contribute to plant UV tolerance and growth. Additionally, we found physical interaction between AtRAD16 and AtRAD7. Thus, the <i>Arabidopsis</i> RAD7/16 complex is functional in plant NER. Furthermore, AtRAD16 makes a significant contribution to <i>Arabidopsis</i> UV tolerance compared to the DDB1/2 and the CSB pathways. This is the first time the role and interaction of DDB1/2, RAD7/16, and CSA/CSB components in a single system have been studied.
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